This invention relates to a composition which produces an exothermic reaction when mixed with water, and to a hot pack containing such a composition, and water isolated therefrom until the intended time for use. By way of illustration but not by way of limitation, particular advantageous embodiments may take the form of a therapeutic hot pack, a hand or foot warmer or a device for heating beverages or packaged or frozen foods. In any case, hot packs per this invention are characterized by an ability to mold and conform to the configuration of the surface to be heated and to provide such surface with an effective level of heat for a period of time up to about twenty minutes.
Compositions for producing an exothermic reaction are known in the prior art. U.S. Pat. No. 3,903,011, for example, discloses a composition producing an exothermic reaction which preferably consists of about 66.7% by weight anhydrous calcium chloride, about 16.7% calcium oxide, about 5.5% guar gum, and about 11.1% anhydrous borax (sodium tetraborate). This composition is activated by adding water in a weight ratio of about 0.55:1 to about 1:1 of water to the dry composition.
The composition of the noted patent must be prepared in a form in which the guar gum and borax encapsulate the calcium oxide and calcium chloride. Upon addition of water, agitation is needed in order to cause the guar gum and borax to form a gel which tends to extend the duration of the exothermic reaction up to about 15 minutes and prevent an extremely rapid temperature rise.
Although the composition of the above mentioned patent has utility in limited applications, a need still exists for a sealed, flexible hot pack providing a moldable structure which readily conforms to the contours of the surfaces to be heated, and wherein the exothermic reaction can be initiated without agitation or mixing to create a gel. To the best of applicant's knowledge no prior art composition or package intended for heating provides such a function which is at the same time completely safe in use and which provides relatively uniform heat over an extended period of time up to about 20 minutes.